1. Field of the Invention
The invention, in general, relates to a novel method of detecting flaws in the surface structure of an object and, more particularly, to a method of detecting flaws in the structure of a surface by comparison with a flawless surface stored in an artificial neuronal net as a virtual master. Preferably, the invention is applied to such tasks as measuring errors which are very small relative to the size of the test object and where for reasons of economic efficiency the measuring position of the test object can only be adjusted with only a low degree of accuracy. Such measuring tasks are encountered, for instance, in monitoring the production of large surface deep drawn sheet components.
2. The Prior Art
A method is known from German patent specification DE 197 53 620.4 C in which three-dimensional measuring data of the surface of a test object are modified by an artificial neuronal net as a virtual master as if three-dimensional measuring data were generated of a flawless test object. By comparing the original three-dimensional measuring data against the artificially generated three-dimensional measuring data flaws, errors and deviations can be detected in the surface.
It is however, a drawback that for detecting flawed spots it is necessary to define three-dimensional data which explicitly characterize the surface structure. These three-dimensional data are often calculated on the basis of digital image data which also characterize, however implicitly, the surface structure including its flawed spots. For the detection of the flawed spots this form of surface characteristic is sufficient.
The complexity of generating three-dimensional measuring data of the surface of the test object is greater as a rule than is the complexity of recording image data. Often the three-dimensional data are calculated on the basis of similar or the same images which in accordance with the invention are utilized directly.
For calculating three-dimensional data of digital images the following methods are particularly well suited: A method of the kind described in DE 196 23 172 C1, a phase shift method of images from two cameras and a the phase shift method utilizing a camera and a projector.
In the calculation of three-dimensional data by one of the mentioned methods it is an important prerequisite that the two cameras or the camera and the projector in the phase shift method are precisely calibrated. This requires additional software. Calibration errors usually result in distortions of the three-dimensional data.
Compared to methods utilizing two cameras, there is a saving of one camera.